For preventing forgery of sheets such as valuable papers, bank notes, documents and the like which carry visible information, there have heretofore been adopted such measures as printing a fine or detailed pictorial pattern and/or characters or the like on the sheet, pasting a hologram on the sheet or impressing a watermark in the sheet while details of these measures being kept in secrecy in an attempt to make it difficult to forge or counterfeit the sheet. Further, inspection of the sheet as to forgery can be carried out by comparing the optical information of printing position on the sheet, fineness of pattern lines, color density or brightness, etc. with the corresponding information of the genuine sheet.
Furthermore, sheet management such as counting of the number(s) of the sheets has heretofore been performed manually or physically with a machine on a sheet-by-sheet basis.
At present, however, technological progress in this field has made it possible to impress the watermark, hologram and the like, and now the information such as mentioned previously can be printed with a high accuracy which is comparable to that of the genuine sheet even though the printing procedure may differ. Such being the circumstances, difficulty is encountered in detecting the forgery solely by relying on the comparison of the optical information.
Additionally, it is noted that in the case of bonds of a same species, the optical information of pictorial pattern or the like which can be used for checking or detecting the forgery remains identical for all the bonds and that the information inherent to the bond such as the bond ID number or the like is not used for the inspection of the forgery. Consequently, once a pictorial pattern of a given bond was counterfeited, there may arise such risky situation that a great number of bonds printed with the counterfeit pattern and having the inherent information such as the ID numbers rewritten are fabricated on a mass-production scale or the contents of the bonds are easily counterfeited.
Besides, in conjunction with such management of the sheets as counting of the number thereof, etc., it is noted that the volume, species, sizes, etc. of the sheets which can be handled at one stretch are limited although it depends on the scale of the managing system. Consequently, a time-consuming troublesome procedure or a large scale of the managing system is required for the management of a large number of sheets. On the other hand, it is also known to manage articles by affixing so-called radio tags onto articles to be managed. However, reliability of the congestion controlling function of the conventional radio tags generally used at present is not so high. Accordingly, employment of the radio tag is not suited for the cases where very high reliability is required as in the case of management of the valuable papers, bank notes and so forth.